The invention relates to a connecting ball joint particularly for an anti-roll bar of a running vehicle, and especially for a bogie and/or body of a high speed train.
In the particular, but nonlimiting, field of anti-roll bars (also known as stabilizing bars or anti-sway bars) commonly used in automotive or rail suspension systems, the function of such a bar is to oppose the vertical forces transmitted to the wheels in bends when the inertia of the vehicle causes the latter to roll transversely.
The means of connecting or of fixing an anti-roll bar to the chassis of the vehicle or to the suspension arms may be varied and, in particular, may comprise bearings or ball joints provided, for example, with an elastic bushing. Such bearings or ball joints have various functions, aside that of fixing the bar to the chassis, such as the function of filtering the forces, during roll, between the structure of the vehicle and the bar, of the function of filtering low-amplitude vibration.
Various types of ball joint exist which allow a certain rotational deflection between two rigid parts. For example, the ball joint may be fitted with a fairly thick rubber or polycarbonate bushing with a frictional connection. It is also possible to anticipate the use of lubricated ball joints.
However, such ball joints are not yet satisfactory because they do not correctly filter vibration, and this leads to unpleasant noise due, for example, to the excessive stiffness of the parts which prevent, or following degradation of the parts which causes play and rattle. They are also not very strong. Finally, they do not have good ratios between angular excursion and stiffness (radial, rotational and conical torsional stiffnesses).
The object of the invention is therefore to solve at least some of these problems.
To do that, the invention relates to a connecting ball joint, for example an anti-roll bar of a running vehicle, said ball joint comprising a straight support running along a general axis of elongation and an elastically deformable member mounted around this support, characterized in that the elastically deformable member comprises at least one laminated structure made up of (a) layer(s) of elastically deformable flexible material and of (a) layer(s) of more rigid material.
In general, the elastically deformable member will comprise means for preloading its laminated structure, particularly for preventing the elastically deformable layer from working in tension.
According to one embodiment, the elastically deformable member may comprise two coaxial annular laminated structures and two annular sleeve tubes each mounted around one laminated structure to preload their elastically deformable layers once these sleeve tubes have been connected together using fixing means, the ball joint then having a plane of section roughly perpendicular to the axis of the support.
In particular, the two sleeve tubes will each have a contact surface perpendicular to the axis of the support and will be welded peripherally at these surfaces.
According to another embodiment, the elastically deformable member may have a plane of section passing through the axis of the support and may comprise two approximately hemispherical laminated structures extending along the axis xxxe2x80x2 and two half sleeve tubes, also approximately hemispherical, each surrounding a laminated structure to preload their elastically deformable layers.
In particular, an outer tube may be crimped around the half sleeve tubes.
In order to allow good angular excursion of the ball joint, while at the same time avoiding having to resort to a lubricant, each laminated structure will consist of an alternation of approximately hemispherical layers of elastically deformable (hyperelastic) flexible material and of approximately hemispherical layers (or cups) of a more rigid material. The good shear properties of rubber are therefore put to full use in order to improve this ability to rotate. Indeed this material has a relatively low shear modulus (of the order of 0.5 to 2 MPa) for a high compression modulus (of the order of 1100 MPa).
Advantageously, each laminated structure will have a hyperelastic flexible layer at each of its ends, one in contact with a spherical core, and the other in contact with the preloading means.
By way of example, the hyperelastic flexible material may be a natural rubber and the rigid material may be a metal, and the layers of flexible material and the layers of rigid material may each have a thickness of the order of 1 mm.
In general, the ball joint also has a radial stiffness higher than the ball joints of the prior art, for equivalent bulk and equivalent possible excursion, and in particular have a radial stiffness which is higher than its torsional and/or torsional conical stiffness.
In addition, the elastically deformable flexible layers are connected to the more rigid layers in such a way that these flexible layers, when subjected to rotational forces about the axis of the support or forces of conical rotation about any axis perpendicular to the axis of the support, experience mainly shear forces, with no slipping with respect to the more rigid layers. Of course, these hyperelastic layers are subjected to radial compressive (and tensile) stresses.
The invention also relates to an anti-roll bar for a running vehicle such as a high speed train, equipped with a connecting ball joint as described hereinabove.